During earth-drilling operations it is common to use a sealed bearing rotary cone drill bit. One common drill bit for use in an earthen annulus includes a bit body having at least one leg, the leg having at least one journal segment. A roller cone is rotatably mounted upon the leg journal segment and forms at least one bearing cavity therebetween. An annular primary seal is disposed between the leg and roller cone and is capable of sealing the bearing cavity. An annular secondary seal is disposed between the leg and roller cone and between the annular primary seal and the earthen annulus. The annular secondary seal is capable of substantially preventing the ingress of debris from the earthen annulus to the annular primary seal.
It is necessary to protect the bearing elements of the bit from contamination in order to sustain bit operability. In particular, it is desirable to isolate and protect the bearing elements of the bit, such as bearings, lubricant and bearing surfaces from earthen cuttings, mud and other debris in the drilling environment. Introduction into the bearing system of such contaminants leads to deterioration of the lubricant, bearings and bearing surfaces, causing undesirable wear and premature bit failure.
It is well known in the art to provide an annular seal around the bearing elements so as to prevent external contaminants from entering the bit through the annular opening and gap formed between each leg and its corresponding cone. These single seal arrangements, however, are known to be susceptible to leakage and premature wear due, for example, to the intrusion and abrasive effect of particles entering through the annular opening. When the single seal fails, the bearing elements become contaminated.
Dual seal arrangements have been developed that have an annular outer seal disposed around a primary inner seal for providing a second layer of protection against particles entering the annular opening. Generally, the outer seals of many prior art dual seal arrangements have provided insufficient protection around the primary seal. When the outer seal fails and allows particles or other contaminants to the primary seal, contamination of the bearing elements can occur as described above. Furthermore, various prior art dual seal arrangements require additional components or internal mechanisms that are susceptible to malfunction and/or increase the complexity of the bit and its manufacturing process.
Attempts have been made to prevent particles from entering the annular opening by directing pressurized drilling fluids, such as air, from within the drill bit out through the annular opening between the leg and cone. U.S. Pat. No. 4,102,419 discloses a rock bit with an inner metal sealing ring and a set of outer hardened mating surfaces between the leg and cone. Fluid is directed from inside the bit, past the inner metal sealing ring and the outer mating surfaces, and out through the annular opening so as to flush cuttings or other debris away from the inner seal. If the exiting fluid flow decreases or ceases, however, the outer mating surfaces may not effectively prevent the ingress of particles to the inner metal sealing ring due to the relative movement between the cone and leg during cone misalignment, thus exposing the inner metal sealing ring to contamination. Hence, for example, if the flow of drilling fluid is turned off during a pause in drilling operations, the particles generated during drilling will fall to the bottom of the hole, where the bit is likely to be sitting. Since there is no fluid flow out of the gap, there is a high probability that some particles will find their way into the annular gap.
It has also been proposed to include a groove in the cone between the inner primary seal and the annular opening. This groove directs fluid from inside the bit out through the annular opening to prevent the entry of particles from the borehole. U.S. Pat. Nos. 4,453,836 and 5,513,711 disclose variations on this concept. Nevertheless, the groove is subject to the same disadvantages, inasmuch as particles that enter the groove during time of reduced fluid flow tend to become trapped in the groove.
Hence, it is believed that the sealed bits of the prior art have significant disadvantages, and there remains a need for more effective configurations for protecting the bearing components of a sealed bearing rotary cone drill bit.